The aim of this multicenter observational study is to determine the prevalence of and the degree to which sleep apnea is an independent or contributing risk factor for the development of cardiovascular or cerebrovascular disease. This application is for a Clinical Center. It is a joint proposal from Cardiovascular Health Study (CHS) at the University of California Davis and the University of Pittsburgh. The population from which participants will be selected includes 2,80& individuals over the age of 66. African Americans make up 20% of the age and gender stratified cohort. Well defined cardiovascular disease prevalence data has been gathered for more than 5 years on most of the cohort. This will allow the identification true incident events. Approximately 1 ,000 study participants will be recruited from the CHS cohort, allowing for stratification by age, race, and gender. Standardized baseline measures of all major cardiovascular risk factors have been obtained. Objective measures of sleep disorders will be gathered in 3 stages: 1) nocturnal pulse oximetry to detect repetitive oxygen desaturation in all participants, 2) eight channel home monitoring of sleep for all those with positive stage 1 tests, and 3) full polysomnography in a local sleep laboratory for a small subset of those with positive stage 2 results. Participants will be closely followed for at least 5 years for cardiovascular morbidity and mortality by CHS. All baseline and follow-up results will be sent to a Data Coordinating Center for analyses.